(a) Field of the Invention
The present invention relates to a method and a system for learning and controlling a torque transmission kiss point of an engine clutch for a hybrid electric vehicle, and more particularly, to a method and a system for learning and controlling a torque transmission kiss point of an engine clutch by gradually increasing hydraulic pressure of the engine clutch around a previous torque transmission kiss point when a uniform relative speed is maintained between an engine and a motor in a no-load state to sense a change of torque of the engine and the motor or a change of a speed of the motor.
(b) Description of the Related Art
In general, a hybrid electric vehicle may reduce exhaust gas and improve fuel efficiency by using a motor as a power source, as well as an engine. In the hybrid electric vehicle, as illustrated in FIG. 1, an engine 11, a driving motor 12, and a transmission 13 may be arranged in series. It should be noted, however, that hybrid electric vehicles may be arranged in many different configurations, including in parallel, in which case the engine and the motor are engaged and disengaged from the transmission accordingly.
In the hybrid electric vehicle 10, an engine clutch 14 for transmitting driving power and blocking the transmission of the driving power may be disposed between the engine 11 and the driving motor 12. FIG. 2 is a conceptual diagram of the engine clutch 14.
As illustrated in FIG. 2, the engine clutch 14 may include a friction material PE moving via pressure (hydraulic pressure) from a fluid (oil) FL of which a quantity is controlled by an operation of a solenoid valve SOL and a return spring SP for restoring the friction material PE to its original state when operation hydraulic pressure is not applied to the friction material PE. The solenoid valve SOL is generally controlled by a current.
The solenoid valve SOL is operated so that hydraulic pressure applied to the friction material PE increases as current applied to the solenoid valve SOL increases. When the hydraulic pressure applied to the friction material PE increases, contact frictional force of the friction material PE increases. Accordingly, as illustrated in FIG. 3, torque transmitted by the engine clutch 14 is increased in proportion to the current applied to the solenoid valve SOL.
In the meantime, in the hybrid electric vehicle 10, an integrated starter and generator (ISG) 15 for operating the engine 11 or serving as a generator may be mounted in the engine 11. The ISG 15 may be called a hybrid starter and generator (HSG) in vehicle manufacturing
The hybrid electric vehicle 10 may run in an electric vehicle (EV) mode that is that utilizes only power from the driving motor 12 to provide a driving force to the transmission and output shaft. Further, the hybrid vehicle 10 may also run in a hybrid electric vehicle (HEV) mode using torque from the engine 11 as main power and torque of the driving motor 12 an auxiliary power. Further, the hybrid electric vehicle 10 may run in a regenerative braking (RB) mode in which braking and inertia energy of the vehicle is collected through power generated by the motor and the battery is charged when the vehicle 10 brakes or runs by inertia.
As described above, the hybrid electric vehicle 10 operates the engine clutch 14 in order to transmit power or separate power between the driving motor 12 and the engine 11 for switching the mode and the like. Operation hydraulic pressure from the engine clutch during an operation of the engine clutch 14 considerably influence drivability, power performance, and fuel efficiency of the hybrid electric vehicle, so that the operation hydraulic pressure of the engine clutch needs to be accurately controlled.
The operation hydraulic pressure of the engine clutch 14 may be determined from the initial hydraulic pressure by which torque is initially transmitted (i.e., a sleep state) and feedback hydraulic pressure for adjusting the hydraulic pressure of the engine clutch 14 by receiving feedback of speeds of the engine 11 and the driving motor 12. More specifically, a sleep state is started as both ends of the friction material PE of the engine clutch 14 come in contact with each other,
The initial hydraulic pressure point at which torque is initially transmitted may be referred to as a kiss point, an initial duty, a biting point, and a dead zone within the vehicle manufacturing field. Current applied at the initial hydraulic pressure point, substantially to the solenoid valve corresponding to the initial hydraulic pressure point, is indicated by KP in FIG. 3.
As illustrated in FIG. 3, the initial hydraulic pressure point KP of the engine clutch 14 corresponds to the point at which torque transmission from the engine clutch is started, so that the engine clutch may substantially transmit the power from this time point. Accordingly, in the present specification, the initial hydraulic pressure point may be called as a torque transmission kiss point or torque transmission kiss point hydraulic pressure for the convenience of description. The torque transmission kiss point exerts significant influence on an operation time and an operation state of the engine clutch 14.
Even though the torque transmission kiss point is optimally set in the engine clutch 14 when a corresponding vehicle is released, the torque transmission kiss point may be changed according to a difference between respective components of the engine clutch, for example, component assembling tolerance, characteristic deviation of current-versus-pressure of the solenoid valve, and characteristic deviation according to passage of usage period. That is, as illustrated by a dotted line in FIG. 3, the torque transmission kiss point may be changed during the use of the engine clutch.
Accordingly, it is necessary to control hydraulic pressure of the engine clutch so that the engine clutch may transmit the torque at an appropriate point in time by learning the torque transmission kiss point of the engine clutch while the hybrid electric vehicle is running.
In a conventional method of learning the torque transmission kiss point, hydraulic pressure at a moment in time at which the engine starts to move by gradually increasing hydraulic pressure applied to the friction material of the engine clutch in a driving state where the engine is stopped and the engine clutch is released, that is, the moment at which a speed of the engine is output, is set as the torque transmission kiss point. However, the conventional art does not consider frictional coefficient deviation of the friction material of the engine clutch, deviation of the return spring, and the characteristic change deviation according to usage. As a result, the conventional learning method is not effective.
Further, in the conventional art, learning may be affected by applying excessive hydraulic pressure characteristics of the pressure while increasing the hydraulic pressure of the engine clutch.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.